1. Field of the Invention
The present invention relates to cell structure and in particular, relates to effects of cell structure on heat dissipation and vibration-proofing nature.
2. Description of the Related Art
To realize a cell with higher power and higher capacity, it is effective to make electrode area larger. Especially when a cell is used as a mobile power source for vehicles, at least 0.1 to 2 m2 of electrode area is required in case of a lithium-ion cell using an electrode with conventional performance.
A cell with large electrode area has required large thickness thereof to secure cell rigidity and easy handling.
On the other hand, a thick cell has posed a problem of excessive temperature elevation in a cell caused by insufficient heat dissipation relative to heat generation in a cell. When temperature is too high in a cell, cell components are decomposed by heat, resulting in promotion of cell degradation. Particularly in case of a bipolar cell, there is a risk that thermal expansion in the cell causes a casing thereof to rupture, resulting in splashing of an electrolyte solution, and this splashed electrolyte sticks to mounted devices, leading to damage thereof. There is another risk, when a thick cell is used at a place liable to receive vibration such as a mobile power source, of undergoing resonance leading to delamination of component layers of a cell.
Cell performance may badly be impaired by degradation of a cell and delamination of component layers. Therefore, it is necessary to take a measure for heat dissipation and vibration-proofing nature of a cell. A conventional method includes a method for suppressing temperature rise in a cell by controlling discharge current quantity and a method for dissipating heat using cooling medium which is disclosed in JP-A-2004-273254. No invention has been found that aims at protection of cell components by lowering vibration of a cell.
In a method for using cooling medium, however, it is necessary to incorporate a structure for arranging thereof and when liquid cooling medium is used, a preventive device against a short circuit of liquid is additionally required. As a result, such a problem arises as increase in cell production steps or requirement of an unnecessarily large cell.
Therefore, it is an object of the present invention to improve heat dissipation and vibration-proofing nature of a cell without using cooling medium while keeping rigidity and discharge current quantity of a cell.